I've never bought an OS before. I put a PC that came with an XP disk some time ago & I've used this ever since on my subsequent builds without problems. But last year we bought MS Office student 2007 for my wife's laptop. 6 months latr the HD failed & I had to replace & re-install everything. This took a second of the three licenses that came with the software. I've installed & registered the 3rd license on my own PC. Now the laptop has gone wrong again. I'm not sure what it is but I'm thinking I may have to re-install everything again, except I've run out of licenses for Office 2007. So do I have to buy it again? If so will the same be true of Windows 7? If I build a new machine or replace the HD will I have to buy it again?!